Network Performance Overview

You learned in the first grade! Everything you need to know about Network Troubleshooting, You learned in the first grade!

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What is Networking? A combination of hardware and software that provides a means for computers in an organization to communicate with one another. No two computer networks are exactly the same No two companies networking needs are exactly the same Each network is continually evolving. Applications, services and technology are changing at a very rapid pace Technology is continually being updated and older technology phased out Users and network support personnel need to continually adapt to the technologies installed at their place of business.

Network Types Local Area Network Building Backbone Campus Backbone Metropolitan Area Network (MAN) Wide Area Network Enterprise Network Connects users in a department, company or work group - Token Ring, Ethernet Connects LANs together in a building ATM, FDDI, Fast Ethernet, Gigabit Ethernet Connects building LANs together Used to connect sites in a large city FDDI, ATM, SONET Used to connect sites across the country ISDN, Frame Relay, T1, T3 All of the above types of networks connected together

MAN

Wide Area Networks (WAN) Designed to connect geographically distant network sites together, although they could be in same city or state Obtained through a service provider (SWBT, SPRINT, AT&T) Use either a leased line or switched circuit technology Usually connect routers together Can use low, or medium speeds like 56 Kbps to 1.544 Mbps (T-1) Use leased lines and pay fixed fee regardless of usage Use circuit switched services where fee is based on usage Examples include Switched 56 Kbps circuits, ISDN, Frame Relay, T-1, X.25, DSL and ATM Protocol Specifications IEEE 802.3 - Ethernet IEEE 802.5 - Token Ring IEEE 802.2 - Logical Link Control Texas Instruments - Token Ring Chipset Intel - Ethernet Chipset ANSI - FDDI Industry Organizations Organization Contact Information Institute of Electrical and Electronics Engineers (IEEE) (800) 678-IEEE Internet Society (703) 648-9888 Network Professional Association (NPA) (800) 214-1973 Sniffer Users Group Check with your local sales office A reading list is provided in the appendix.

Enterprise Networks Is a term used to describe the entire network of a company which has many or all of the following networks connected: Local Area Networks (LAN) Building Backbone Campus Backbone Metropolitan Area Network (MAN) Wide Area Network (WAN) Protocol Specifications IEEE 802.3 - Ethernet IEEE 802.5 - Token Ring IEEE 802.2 - Logical Link Control Texas Instruments - Token Ring Chipset Intel - Ethernet Chipset ANSI - FDDI Industry Organizations Organization Contact Information Institute of Electrical and Electronics Engineers (IEEE) (800) 678-IEEE Internet Society (703) 648-9888 Network Professional Association (NPA) (800) 214-1973 Sniffer Users Group Check with your local sales office A reading list is provided in the appendix.

Networking Components

Basic Network Components There are three basic Network Components The end station The Applications that run on the end stations The network which supports traffic flow between end stations End Stations: PCs, Servers, Workstations, Laptops, Printers, Scanners Applications: File Services, Print Services, Operating Systems, E-mail, Imaging, Fax Networks: Network Operating System (NOS), Ethernet, Token Ring, FDDI, ATM, Fast Ethernet, Frame Relay, ISDN, DSL, T-1, Switches, Bridges, Routers, Hubs

Network Bandwidth Networks have a finite bandwidth or capacity that can be used by the particular network. Most of the LAN topologies use a shared media access control protocol Ethernet - CSMA/CD - Carrier Sense Multiple Access / Collision Detection 10 Mbps, 100 Mbps, 1Gbps Token Ring - MAC - Media Access Control 4 Mpbs, 16 Mpbs FDDI - SMT - Station Management 100 Mbps

The Internet Uses TCP/IP as the common transport protocol Developed out of the US Government ARPANET Supports access around the world to both public and private users (VPN) Virtual Private Networks Some of the applications that run on the Internet include: World Wide Web (WWW) - application that allows access to different types of data including text, audio and video. File Transfer Protocol (FTP) - application that allows files to be transferred from one computer to another Simple Mail Transfer Protocol (SMTP) - application that provides electronic mail (email) to be sent from user to user.

Accessing the Internet The Internet is a computer network that connects many networks together and is built upon a tiered architecture Tier 1 - National Access Points (NAP) - Regional interchange facility which connects networks in an area using routers Tier 2 - National Service Providers (NSP) - Connect National Access Points together Tier 3 - Internet Service Providers (ISP) - Provide Internet access to commercial and private users

The OSI Model

The OSI Reference Model Host A Host B Allows users to transfer files, send mail, etc. Only layer that users can communicate with directly Key features are ease of use and functionality Standardized data encoding and decoding Data compression Data encryption and decryption Manages user sessions Reports upper-layer errors Supports Remote Procedure Call activities Connection management Error and flow control Provides reliable, efficient service Inter-network packet routing Minimizes subnet congestion Resolves differences between subnets Network access control Packet framing Moves bits across a physical medium Interface between network medium and interface devices Defines electrical and mechanical characteristics of LAN 7 Application Application Provides Services Connects processes Moves Data 6 Presentation Presentation 5 Session Session Transport 4 Transport 3 Network Network 2 Data Link Data Link 1 Physical Physical

Frame Headers Frames headers revolve around the OSI model. DLC * LLC Network Transport Application Frames headers revolve around the OSI model. The protocol headers are used to move the data. How many bytes is the DLC Header How about the IP header Good, now how about the TCP header *The number of headers in a frame is protocol-dependent. There are many good reference books and classes specific to protocols, a good reference site is www.protocols.com

Network Communication Each layer of the OSI model provides a specific communications function and each layer should be independent of its adjacent layers A header, created by each layer, implements the function for that layer. The combination of header and data is called a Protocol Data Unit (PDU) When the PDU created by the Network layer reaches the Data Link layer, both a header and trailer are added and this creates a frame When the frame from Host A reaches Host B, each header that was added by a layer in Host A determines the action taken by the peer layer on Host B

Protocols Computers on networks use protocols to communicate and these protocols define the procedures that each system involved in the communications process will use. Protocols are a set of procedures that are agreed upon and then followed by each communicator Protocols are combined into what is called a communication architecture or protocol stack Each protocol in the architecture provides a function that is necessary to make data communications possible Generally, there are two types of protocols: Connectionless Protocols Connection Oriented Protocols

Connectionless Protocols Simply send data from a source address to a destination address No verification is performed to determine if the destination address is available. Connectionless protocols are generally referred to as Datagram Service Much like sending a postcard via the US Mail Datagram protocols usually do not support error recovery or any type of acknowledgement routine classifying them as an unreliable transmission service - (not to be confused with the USPS) Connectionless protocols are typically used because of efficiency and because the data being sent does not justify the extra overhead necessary to perform the error recovery or acknowledgment routine. Example: TCP/IP’s - UDP (User Datagram Protocol), SNMP (Simple Network Management Protocol)

Connection Oriented Protocols A Connection Process or handshake is implemented between two stations before the transmission of data occurs Connections are referred to as sessions, virtual circuits, or logical connections Most connection oriented protocols require some form of acknowledgement as data is transmitted, this is the mechanism that provides reliable data transmission over the network When data is found to be in error, the sending side is asked to re-transmit the frame, or if the sender has not received an Acknowledgement, it will re-transmit after a specific amount of time When the connection is no longer needed, there is a defined disconnect process Example: TCP/IP’s - TCP (Transport Control Protocol), SPX (Sequenced Packet Exchange), SDLC

IP Internet Protocol

What Does IP Do? Delivers packets across a network. Delivery is based on IP address. Route frames from one network to another. IP does not provide flow control or error control, but can provide Type of Service (Quality of Service). IP fragments and re-assembles frames for traversal across networks that require small frames (X.25) based on the Maximum Transmission Unit (MTU) size.

IP Functionality Server Client Router APP TCP IP MAC APP TCP IP MAC IP Subnet 1 IP Subnet 2 MAC MAC Frames get sent to the MAC address of the Router. The Router strips the DLC and builds new frame to put on other subnet. Router also decrements the Time to Live (TTL) field, calculates the new checksum.

IP Fragmentation and Reassembly

TCP Transport Control Protocol

The 4 Layer Internet Model Application Message 3 Transport Segments 2 Network Packets 1 Frames Local Network

Addressing in TCP/IP Application “Messages” Process I.D. Specifies a Host Process Transport “Segments” Specifies a TCP Port Port Address Network Socket “Packets & Datagrams” Specifies a Logical IP Address Network Device Data Link Specifies a SAP “Frames” LLC Address Specifies a DLC Mac (DLC) Address Network Device Physical Bits

What Does TCP Offer? Reliable Packet Delivery Flow Control Sequence Number + TCP Length = Acknowledgment or Sequence Number + TCP Length = Next Sequence Number Retransmission of Data (Lost Frame, Dropped Frame, CRC error in frame) Flow Control Using Sliding Windows Positive Acknowledgement with Retransmission Multiplexing of Conversations or Connections Error Control (TCP Header Checksum)

When did you learn to dial a phone? Virtual Network Circuit Collect Call from ABC, do you accept the charges? Yes = (3 way handshake) (SYN) No = Reset Connection (RST)

What is a Port? Virtual Circuit Identifier Workstation Server “Client’s” use an “ephemeral” port (Short Lived, for the duration of the connection). Client ports are typically above 1023. “Servers” use the “well-known” port or listening port. Usually these ports are defined between 0 – 1023. See www.iana.org for list of ports

What is a Connection? The Virtual Circuit Workstation Server Port 1518 Port 23 198.54.18.23 198.54.18.3 The IP address and TCP port number of one application process (sometimes called a “socket”) is associated with the “socket” of another application process, creating a pair of addresses used to refer to the connection. All data transfers are tracked through the socket pairing, which defines the virtual circuit being used during the duration of the connection.

TCP Connection SYN SYN SYN RST ACK

Connection Establishment “Three-Way Handshake” Client Server Send SYN (SEQ = X) WIN = size Max Segment Size = 1024 1 Receive SYN Send SYN (SEQ = Y)/ACK (X + 1) WIN = size Max Segment Size = 1024 2 Receive SYN/ACK Segment Send ACK (Y + 1) 3 Receive ACK Segment

Reliability

Reliability

Reliability Positive Acknowledgment with Retransmission (PAR) Server Workstation Positive Acknowledgment with Retransmission (PAR) Packet “Client” must receive ACK before the retransmission timer expires. Otherwise, packet will be re-transmitted. Acknowledgement Sliding Window Seq = 1 + Len=1024 Seq = 1025 + Len=1024 Acknowledgement = 2049

Segment Size affects Performance Small Segments Large Segments 54B 12 K Bytes 54B 12B Header Data Header Data Header Data Header over 4x Data; therefore, only 1/4 of Network Bandwidth is being used. 54B 1.5KB 54B 1.5KB 54B 1.5KB Header Data Header Data Header Data Increases response time because of fragmentation time. Maximum Frame Size = 1518

Putting it all together!

Simple Information to Gather! Network Statistics Average Network Utilization Total Frames Total Bytes Average Frame Size Packet Drops Interface Errors Top Talkers #1 Station % Usage #2 Station % Usage #3 Station % Usage Top Protocols Protocol #1 % Protocol #2 % Protocol #3 % Response Times NCP / SMB Create File Cmd/Resp NCP / SMB File Read Cmd/Resp NFS Create File Cmd/Resp TCP Session Establishment DNS Request/Reply DHCP initialization time Telnet Cmd/Echo/Ack Gather this information from each subnet, building or geographic location.