1. Wide Area Network A Wan is a data Communication network that covers a relatively broad geographical area and that often uses transmission facilities provided by common carriers, such as telephone companies

2. WAN Devices WANs use numerous types of devices that are specific to WAN environments. WAN switches, access servers, modems, CSU/DSUs, and ISDN terminal adapters are discussed in the following sections. Other devices found in WAN environments that are used in WAN implementations include routers, ATM switches, and multiplexers.

3. WAN Switch  A WAN switch is a multiport internetworking device used in carrier networks. These devices typically switch such traffic as Frame Relay, X.25, and SMDS, and operate at the data link layer of the OSI reference model. Figure 3-5 illustrates two routers at remote ends of a WAN that are connected by WAN switches.  Figure 1.0 Two Routers at Remote Ends of a WAN Can Be Connected by WAN Switches

4. Figure 1.0

5. Access Server  An access server acts as a concentration point for dial-in and dial-out connections. Figure 3- 6 illustrates an access server concentrating dial-out connections into a WAN.  Figure 1.2 An Access Server Concentrates Dial-Out Connections into a WAN

6. Figure 2.0

7. Modem  A modem is a device that interprets digital and analog signals, enabling data to be transmitted over voice-grade telephone lines. At the source, digital signals are converted to a form suitable for transmission over analog communication facilities. At the destination, these analog signals are returned to their digital form. Figure 3-7 illustrates a simple modem-to-modem connection through a WAN.  Figure 3 A Modem Connection Through a WAN Handles Analog and Digital Signals

8. Figure 3.0

9. CSU/DSU  A channel service unit/digital service unit (CSU/DSU) is a digital-interface device used to connect a router to a digital circuit like a T1. The CSU/DSU also provides signal timing for communication between these devices. Figure 4.0 illustrates the placement of the CSU/DSU in a WAN implementation.  Figure4.0The CSU/DSU Stands Between the Switch and the Terminal

10. Figure 4.0

11. ISDN Terminal Adapter  An ISDN terminal adapter is a device used to connect ISDN Basic Rate Interface (BRI) connections to other interfaces, such as EIA/TIA- 232 on a router. A terminal adapter is essentially an ISDN modem, although it is called a terminal adapter because it does not actually convert analog to digital signals. Figure 5.0 illustrates the placement of the terminal adapter in an ISDN environment.  Figure5.0The Terminal Adapter Connects the ISDN Terminal Adapter to Other Interfaces

12. Figure 5.0

13. Wan Connection Types 13 There are four types of Wan Connectivity : Dedicated Lines Circuit Switching Packet Switching Broadband

14. Dedicated lines 14 Dedicated Lines It simulates a single cable connection between the local and remote site Used for shorter to medium distances and for longer connectivity. Leased lines are pre-established wan communication path from dte to dce switch and again from dce switch to remote’s dte from communtion with out any setup before sending data. Private line Bandwidth is fixed Line is 24hrs up Whether used or not billing is done eg: Leased Lines

15. Circuit switching 15 Circuit Switching The term circuit switching means phone call Used for medium to longer distances and for shorter connectivity. It is used for low bandwith data transfer & bandwidth is fixed Billing Depends upon the Usage No data is transfer before the end to end connection is established Circuit switch technology uses dialup modems or isdn connections eg: ISDN, PSTN (Dial Up connections)

16. Differnce between Pstn & Isdn Pstn[Public switched telephone network]. Analog signals Slow speed 28.8 kbps Either Voice or data. Isdn[intergrated services digital network] Digital signals Speed up to 128kbps Voice and data at a time simultaneously

17. Packet Switching 17 Packet Switching Packet switched connections use logical circuits to make connection between two sites. These logical circuits are refered to as [Vc’s] a logical circuit is build across any built physical circuit. In packet switch using one interface u can connect to multiple interfaces. Used for medium to longer distances and for longer connectivity. Bandwidth is shared eg: Frame-Relay

18. Broadband & X DSL Broadband:- Same functions as X Dsl but here internet and telephone can’t be used simultaneously only one at a time. First broadband came then it turned into X-Dsl X Dsl :- (digital subscriber line) here X means it may be either A,B,C i.e. X. It is dedicated, cheaper, fast, telephone and intranet can be used at a time simultaneously.

19. Difference between DTE and DCE DCE  Data communication equipment  Generating, clocking (i.e., speed)  Master  Example of DCE devices in leased line setups: V.35 and G703 modem and exchange (MODEM and MUX) (MUX – Multiples)  Example of DCE devices in dial-up setup: dialup modem DTE  Data terminal equipment.  Accept clocking (i.e., speed).  Slave.  Example of DTE devices in leased setup: router  Example of DTE devices in dial up setup: computer

20. Wan connection Communication methods  Leased lines  Isdn / Pstn  X DSL /broadband  Vsat [very small aperture terminal]  Radio/Wireless Wan protocols  Hdlc  PPP  Frame-relay  Atm  X.25

21. Wan protocols PPP  Point to Point Protocol  Open Standard Protocol (works with same and different company Routers i.e. Cisco– Nortel, Cisco–Multicom.  Supports Authentication  Supports Compression HDLC  High level Data link Control  Vendor proprietary Protocol (works with same company Router only, i.e. Cisco-Cisco, Nortel-Nortel, etc.)  No Support for Authentication  No Support for Compression

22. 22 Wan Interface Configuration E0 10.0.0.1/8 HYD E0 20.0.0.1/8 1.1.1.1/8 S0 S1 1.1.1.2/8

23. 23 ================================ Welcome to Hyderabad Router ================================ User Access Verification password : **** **** enable show controllers S 0 Hyderabad> password : Hyderabad# Microsoft Windows 2000 [Version 5.00.2195] (C) Copyright 1985-2000 Microsoft Corp. C:\> Connecting..... HD unit 0, idb = 0xB7574, driver structure at 0xBC2F8 buffer size 1524 HD unit 0, V.35 DCE cable cpb = 0x1, eda = 0x4940, cda = 0x4800 RX ring with 16 entries at 0x4014800 00 bd_ptr=0x4800 pak=0x0BE054 ds=0x401B6A8 status=80 pak_size=0 01 bd_ptr=0x4814 pak=0x0BED04 ds=0x401E5B0 status=80 pak_size=0 02 bd_ptr=0x4828 pak=0x0BE224 ds=0x401BD60 status=80 pak_size=0 03 bd_ptr=0x483C pak=0x0BEED4 ds=0x401EC68 status=80 pak_size=0 --More-- telnet 10.0.0.1

24. 24 04 bd_ptr=0x4850 pak=0x0BEB34 ds=0x401DEF8 status=80 pak_size=0 05 bd_ptr=0x4864 pak=0x0BF0A4 ds=0x401F320 status=80 pak_size=0 06 bd_ptr=0x4878 pak=0x0BDE84 ds=0x401AFF0 status=80 pak_size=0 07 bd_ptr=0x488C pak=0x0BE794 ds=0x401D188 status=80 pak_size=0 08 bd_ptr=0x48A0 pak=0x0BDCB4 ds=0x401A938 status=80 pak_size=0 09 bd_ptr=0x48B4 pak=0x0BE964 ds=0x401D840 status=80 pak_size=0 10 bd_ptr=0x48C8 pak=0x0BE3F4 ds=0x401C418 status=80 pak_size=0 11 bd_ptr=0x48DC pak=0x0BDAE4 ds=0x401A280 status=80 pak_size=0 12 bd_ptr=0x48F0 pak=0x0BD914 ds=0x4019BC8 status=80 pak_size=0 13 bd_ptr=0x4904 pak=0x0BD744 ds=0x4019510 status=80 pak_size=0 14 bd_ptr=0x4918 pak=0x0BD574 ds=0x4018E58 status=80 pak_size=0 15 bd_ptr=0x492C pak=0x0BD3A4 ds=0x40187A0 status=80 pak_size=0 16 bd_ptr=0x4940 pak=0x0BD1D4 ds=0x40180E8 status=80 pak_size=0 cpb = 0x1, eda = 0x5014, cda = 0x5014 TX ring with 2 entries at 0x4015000 00 bd_ptr=0x5000 pak=0x000000 ds=0x4031838 status=80 pak_size=22 01 bd_ptr=0x5014 pak=0x000000 ds=0x000000 status=80 pak_size=0 02 bd_ptr=0x5028 pak=0x000000 ds=0x000000 status=80 pak_size=0 0 missed datagrams, 0 overruns 0 bad datagram encapsulations, 0 memory errors 0 transmitter underruns 0 residual bit errors Hyderabad#

25. 25 ================================ Welcome to Chennai Router ================================ User Access Verification password : **** **** enable show controllers S 1 Chennai> password : Chennai# Microsoft Windows 2000 [Version 5.00.2195] (C) Copyright 1985-2000 Microsoft Corp. C:\> Connecting..... HD unit 0, idb = 0xB7574, driver structure at 0xBC2F8 buffer size 1524 HD unit 0, V.35 DTE cable cpb = 0xE1, eda = 0x4814, cda = 0x4828 RX ring with 16 entries at 0xE14800 00 bd_ptr=0x4800 pak=0x0BEB34 ds=0xE1DEF8 status=80 pak_size=13 01 bd_ptr=0x4814 pak=0x0BF0A4 ds=0xE1F320 status=80 pak_size=13 02 bd_ptr=0x4828 pak=0x0BED04 ds=0xE1E5B0 status=80 pak_size=0 03 bd_ptr=0x483C pak=0x0BE964 ds=0xE1D840 status=80 pak_size=0 --More-- telnet 20.0.0.1

26. 26 04 bd_ptr=0x4850 pak=0x0BE794 ds=0xE1D188 status=80 pak_size=0 05 bd_ptr=0x4864 pak=0x0BE5C4 ds=0xE1CAD0 status=80 pak_size=0 06 bd_ptr=0x4878 pak=0x0BE3F4 ds=0xE1C418 status=80 pak_size=0 07 bd_ptr=0x488C pak=0x0BE224 ds=0xE1BD60 status=80 pak_size=0 08 bd_ptr=0x48A0 pak=0x0BE054 ds=0xE1B6A8 status=80 pak_size=0 09 bd_ptr=0x48B4 pak=0x0BDE84 ds=0xE1AFF0 status=80 pak_size=0 10 bd_ptr=0x48C8 pak=0x0BDCB4 ds=0xE1A938 status=80 pak_size=0 11 bd_ptr=0x48DC pak=0x0BDAE4 ds=0xE1A280 status=80 pak_size=0 12 bd_ptr=0x48F0 pak=0x0BD914 ds=0xE19BC8 status=80 pak_size=0 13 bd_ptr=0x4904 pak=0x0BD744 ds=0xE19510 status=80 pak_size=0 14 bd_ptr=0x4918 pak=0x0BD574 ds=0xE18E58 status=80 pak_size=0 15 bd_ptr=0x492C pak=0x0BD3A4 ds=0xE187A0 status=80 pak_size=0 16 bd_ptr=0x4940 pak=0x0BD1D4 ds=0xE180E8 status=80 pak_size=0 cpb = 0xE1, eda = 0x5028, cda = 0x5028 TX ring with 2 entries at 0xE15000 00 bd_ptr=0x5000 pak=0x000000 ds=0xE31964 status=80 pak_size=13 01 bd_ptr=0x5014 pak=0x000000 ds=0xE31964 status=80 pak_size=13 02 bd_ptr=0x5028 pak=0x000000 ds=0x000000 status=80 pak_size=0 0 missed datagrams, 0 overruns 0 bad datagram encapsulations, 0 memory errors 0 transmitter underruns 0 residual bit errors Chennai#

27. 27 telnet 192.168.1.150 ================================ Welcome to Hyderabad Router ================================ User Access Verification password : **** **** enable configure terminal interface serial 0 ip address 10.0.0.1 255.0.0.0 no shutdown clockrate 64000 encapsulation hdlc Hyderabad> password : Hyderabad# Enter configuration commands, one per line. End with CNTL/Z. Hyderabad(config)# Hyderabad(config-if)# Microsoft Windows 2000 [Version 5.00.2195] (C) Copyright 1985-2000 Microsoft Corp. C:\> Connecting..... Configuring Serial interface Router(config)#interface serial Router(config-if)#ip address Router(config-if)#no shutdown Router(config-if)#clockrate Router(config-if)#encapsulation {ppp|hdlc} Configuring Serial interface Router(config)#interface serial Router(config-if)#ip address Router(config-if)#no shutdown Router(config-if)#clockrate Router(config-if)#encapsulation {ppp|hdlc} exit Hyderabad(config)#

28. 28 ================================ Welcome to Chennai Router ================================ User Access Verification password : **** **** enable configure terminal ip address 10.0.0.2 255.0.0.0 no shutdown encapsulation hdlc exit Chennai> password : Chennai# Enter configuration commands, one per line. End with CNTL/Z. Chennai(config)# Chennai(config-if)# Chennai(config)# Microsoft Windows 2000 [Version 5.00.2195] (C) Copyright 1985-2000 Microsoft Corp. C:\> Connecting..... Configuring Serial interface Router(config)#interface serial Router(config-if)#ip address Router(config-if)#no shutdown Router(config-if)#clockrate Router(config-if)#encapsulation {ppp|hdlc} Configuring Serial interface Router(config)#interface serial Router(config-if)#ip address Router(config-if)#no shutdown Router(config-if)#clockrate Router(config-if)#encapsulation {ppp|hdlc} telnet 192.168.2.150 interface serial 1

29. 29 Hyderabad(config-if)# telnet 192.168.1.150 ================================ Welcome to Hyderabad Router ================================ User Access Verification password : **** enable configure terminal interface serial 0 ip address 10.0.0.1 255.0.0.0 no shutdown clockrate 64000 encapsulation hdlc Hyderabad> password : Hyderabad# Enter configuration commands, one per line. End with CNTL/Z. Hyderabad(config)# Hyderabad(config-if)# Microsoft Windows 2000 [Version 5.00.2195] (C) Copyright 1985-2000 Microsoft Corp. C:\> Connecting..... exit Hyderabad(config)# exit Hyderabad# show int s0

30. 30 Serial0 is up, line protocol is up Hardware is HD64570 Internet address is 10.0.0.1/8 MTU 1500 bytes,BW 1544 Kbit,DLY 20000 usec,rely 255/255,load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:05:29, output 00:00:03, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 997 packets input, 20161 bytes, 0 no buffer Received 875 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 899 packets output, 24785 bytes, 0 underruns 0 output errors, 0 collisions, 132 interface resets 0 output buffer failures, 0 output buffers swapped out 325 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up Hyderabad# show int s0 1.Serial0 is up, line protocol is up All configurations and the connectivity are perfect on both the routers. 1.Serial0 is up, line protocol is up All configurations and the connectivity are perfect on both the routers.

31. 31 Serial0 is administratively down, line protocol is down Hardware is HD64570 Internet address is 10.0.0.1/8 MTU 1500 bytes,BW 1544 Kbit,DLY 20000 usec,rely 255/255,load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:01:27, output 00:01:20, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 995 packets input, 20133 bytes, 0 no buffer Received 873 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 896 packets output, 24163 bytes, 0 underruns 0 output errors, 0 collisions, 131 interface resets 0 output buffer failures, 0 output buffers swapped out 325 carrier transitions DCD=up DSR=up DTR=down RTS=down CTS=up Hyderabad# 2.Serial0 is administratively down, line protocol is down No Shutdown (Layer1 command) is not given on the local router’s serial interface. 2.Serial0 is administratively down, line protocol is down No Shutdown (Layer1 command) is not given on the local router’s serial interface. show int s0

32. 32 Serial0 is up, line protocol is down Hardware is HD64570 Internet address is 10.0.0.1/8 MTU 1500 bytes,BW 1544 Kbit,DLY 20000 usec,rely 255/255,load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:07:56, output 00:00:05, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 1028 packets input, 20595 bytes, 0 no buffer Received 906 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 917 packets output, 25475 bytes, 0 underruns 0 output errors, 0 collisions, 138 interface resets 0 output buffer failures, 0 output buffers swapped out 341 carrier transitions DCD=up DSR=up DTR=up RTS=up CTS=up Hyderabad# 3.Serial0 is up, line protocol is down i)Encapsulation or Clock Rate(Layer2 commands) is not given ii) Encapsulation mismatch. 3.Serial0 is up, line protocol is down i)Encapsulation or Clock Rate(Layer2 commands) is not given ii) Encapsulation mismatch. show int s0

33. 33 Serial0 is down, line protocol is down Hardware is HD64570 Internet address is 10.0.0.1/8 MTU 1500 bytes,BW 1544 Kbit,DLY 20000 usec,rely 255/255,load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input 00:12:40, output 00:00:08, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 1088 packets input, 21435 bytes, 0 no buffer Received 966 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 945 packets output, 26091 bytes, 0 underruns 0 output errors, 0 collisions, 147 interface resets 0 output buffer failures, 0 output buffers swapped out 370 carrier transitions DCD=down DSR=down DTR=up RTS=up CTS=down Hyderabad# 4.Serial0 is down, line protocol is down i) No Shutdown is not given on the remote router’s interface ii) Some problem with the physical connectivity. 4.Serial0 is down, line protocol is down i) No Shutdown is not given on the remote router’s interface ii) Some problem with the physical connectivity.

34. Trouble shooting Hyd#show int S0 If serial 0 is up, line protocol is up. It implies all configurations and the connectivity are fine. If serial 0 is administratively down, line protocol is down. Implies, no shutdown (layer 1 command) has not been given on the local router interface. If serial 0 is up and line protocol is down. Implies, encapsulation or clock rate (layer 2 command) have not been given or encapsulation on both the routers are different. Serial 0 is down and line protocol is down. Implies, no shutdown command has not been given on the remote router interface or some problem with the physical connectivity.

35. PPP Authentication 35 PPP Authentication In PPP two types of Authentication : PAP - Password Authentication Protocol 2 Way Handshaking protocol Username and password are sent in clear text No Security CHAP- Challenge Handshake Authentication protocol 3 Way Handshaking protocol Username is sent in clear text and Password in encrypted form Secure

36. Configure WAN protocols between R1 and R2 R1 Step1:- Router(config)#int s0 Router(config)#ip address 1.1.1.1 255.0.0.0 Step2:- Router(config-if)encapsulation ppp R2 Step1:- Router(config)#int s0 Router(config-if)#ip address 1.1.1.2 255.0.0.0 Step 2:- Router(config-if)#encapsulation ppp Verification:Show interface Serial 0

37. Configuration ppp Authentication CHAP Step1:- Router(config)#int so Router(config-if0#ip address 1.1.1.1 255.0.0.0 Step2:- Router1(config)#username router1 password cisco123 Router(config-if)#Encapusulation ppp. Router(config-if)#ppp authentication chap Step1:- Router(config)#int so Router(config-if0#ip address 1.1.1.12 255.0.0.0 Step2:- Router2(config)#username router1 password cisco 123 Router(config-if)#Encapusulation ppp. Router(config-if)#ppp authentication chap

38. Configuration ppp Authentication CHAP Verification Ping 1.1.1.2 Router#Debug ppp authentication Router#config t Router(config)# int s0 Router (config-if)#Shut Router (config-if)#no shut Verification Ping 1.1.1.1 Router#Debug ppp authentication Router#config t Router(config)# int s0 Router (config-if)#Shut Router (config-if)#no shut

39. Configuration ppp Authentication PAP Step1:- Router(config)#int so Router(config-if)#ip address 1.1.1.1 255.0.0.0 Step2:- Router(config)#username abc password 123 Step3:- Router(config)#int so Router(config-if)#Encapusulation ppp. Router(config-if)#ppp authentication pap Router(config-if)# Ppp pap sent- username xyz pass 321 Step1:- Router(config)#int so Router(config-if0#ip address 1.1.1.2 255.0.0.0 Step2:- Router(config)#username xyz password 321 Step3:- Router(config)#int so Router(config-if)#Encapusulation ppp. Router(config-if)#ppp authentication pap Router(config-if)# Ppp pap sent- username abc pass 123

40. Configuration ppp Authentication PAP Verification Ping 1.1.1.2 Router#Debug ppp authentication Router#config t Router(config)# int s0 Router (config-if)#Shut Router (config-if)#no shut Verification Ping 1.1.1.1 Router#Debug ppp authentication Router#config t Router(config)# int s0 Router (config-if)#Shut Router (co nfig-if)#no shut

41. Frame Relay 41 Frame Relay is a data link layer packet-switching protocol that uses digital circuits. It is used for medium to longer distances and for longer connectivity. Leased lines also provide longer connectivity but a physical circuit is used to make connection between 2 sites and the same circuit path is used always. Frame Relay connections use logical circuits to make connections between 2 sites. These logical circuits are referred to as Virtual Circuits(VCs). Multiple VCs can exist on the same physical connection. VCs are Full duplex. Frame Relay

42. Advantage of frame relay 42 VCs overcome the scalability problems of leased lines by providing multiple logical circuits over the same physical connection. Only one serial interface of a router is needed to handle the VC connections to multiple sites Whereas using leased lines multiple serial interfaces are needed to connect to multiple sites. VCs provide full connectivity at a much lower price compared to leased lines. Advantages of Frame Relay

43. Frame Relay Technology 43 Sub-interfaces Uses Shared bandwidth Local Management interface(LMI): –used between the Frame relay DTE(eg.Router) and the Frame Relay DCE(eg. Frame Relay switch) –Defines how the DTE interacts with the DCE –Locally significant –Provides VCs status information(a keep-alive mechanism) –LMI standards : Cisco, ANSI, Q933a The DTE and DCE must have the same LMI signaling type Frame Relay Terminology

44. Frame Relay Terminolgy 44  Data Link Connection Identifier(DLCI) :  used to identify each VC on a physical interface (i.e.) Each VC has a unique local address called a DLCI number.  switch will map to the destination depending on the DLCI number  Inverse ARP is used to map DLCIs to next hop addresses.  Mapping can also be done manually.  Its Locally significant.  These numbers are given by the Frame relay service providers, Service providers assign DLCIs in the range of 16 to 1007. Frame Relay Terminology

45. 45  Virtual circuits are of two types:  Permanent Virtual Circuits – PVCs  Switched Virtual Circuits –SVCs  Permanent Virtual Circuit :  similar to a dedicated leased line, permanent connection.  used when constant data is being generated.  Switched Virtual Circuit :  also called as Semi-permanent virtual circuit  similar to a circuit switched connection where the VC is dynamically built and then torn down once the data has been sent.  used when data has to be sent in small amounts and at periodic intervals. Frame Relay Terminology

46. 46  Committed Information Rate(CIR) :  Average data rate measured over a fixed period of time that the carrier guarantees for a VC.  committed bandwidth  Burst Rate(BR) :  Average data rate provider guarantees for a VC.  Excess bandwidth Frame Relay Terminology

47. 47  FECN and BECN :  Forward Explicit Congestion Notification  Backward Explicit Congestion Notification  When congestion occurs switch marks the FECN and BECN bits in the frame header.  FECN is sent to the destination  BECN is sent to the source  Thereby notifying both source and destination about the congestion.  FECN = 0 and BECN =0 implies no congestion. Frame Relay Terminology