Campus Area Networking

Technologies for routing packets from one LAN to another

Layer 3 Communication

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Network - Layer 3

The network layer establishes the route between the sending and receiving stations. The node to node function of the data link layer (layer 2) is extended across the entire internetwork, because a routable protocol contains a network address in addition to a host address.

Application

Presentation

Session

Transport

Network

Data Link

Physical

©”A Guide to Networking Essentials”, 1998, Course Technology.

OSI Reference Model

Routing

BODY

Layer 3Header

Layer 2Trailer

Layer 2Trailer

Routers read packets up to layer 3

Network Routing

Protocols for internetworking.

Two major types

Packet switching (or datagram) Usually layers 3 and 4

Circuit switching Usually layers 1 and/or 2

Packet switching or Datagram Protocols

Best effortFrames take individual routesPacket assembly devices neededError ControlTraffic Management

Buffering Discard

Node Functions

Message forwardingError detection and correctionTraffic management

Router Functions

Routers perform layer 1, 2, and 3 functions Packet passing

Error correction

Message routingIncluding circuit definition

Protocol translation Firewall functions(see the tracert function on the TCP/IP stack)

Switches and Routers

SwitchExecutes in

firmwareNot flexibleFast executionInexpensive

RouterExecutes in softwareFlexibleSlow executionExpensive

Any logic that can be executed in software can also be converted to firmware using ASIC technology (application specific integrated circuits).

Routers

Input Buffer

ProcessorOutput Buffer

From A From B

To C To D

Table ofAddresses

Input Buffer

Input BufferOutput Buffer

Packet Routing

Datagram Packets proceed along their own route

and must be reordered at the end.Circuit

Packets all take the same route and arrive in order

Datagram Logic (IP)

Packet n Packet 1Packet 2

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IP

Best EffortAddressingVariable packet lengths (1500 bytes

or less)IPv4 vs IPv6Frame and Header

The Internet:IP Addressing – IP v4

32 bits (4 bytes) Network address + Host address in one

Classes (originally) A: 126 nets, 3 bytes of client

addresses B: 2 bytes of client addresses (e.g. OU) C: 1 byte of client addresses (256)

Next step – IPv6 128 bit address space Why?

IP Header (Layer 3)

Version =4

Header length In bytes

Type of service Characteristic of route

Total length Length of the packet

Source port identifier Port identifier for host process

Fragment offset Position (8 byte units) from message start

Time to live Allowed seconds

Protocol ID of Transport layer protocol (TCP = 6)

Header checksum

Source address 32 bits

Destination address 32 bits

Options + Padding

Data

How IP Routing Works

IPRouting

Circuit Protocols

All packets take the same routeNo packet assembly device to reorder

packetsNormally layer 2 connectionMay be permanent or switchedAllow guaranteed service quality levelsMay be used to carry datagram

protocols

Circuit Logic

Source Destination

Setup

Message & ACK’s

Teardown

Frame Relay

Frames relayed without reconstruction

End to end error control using CRC error detection at layer 3 level

Variable packet sizeVirtual circuit (usually permanent)Multiple data ratesMultiple quality levels

Frame Relay Pricing Components

Port speed Measured as Maximum Bit Rate

(56K, T1, etc.) Up to DS3 speed (45 Mbps)

Processing quality Access (lowest) Burst Committed

Frame Relay Processing Quality

Asynchronous Transfer Mode – layer 2 networking

Cell switchedEqual length cells – 53 bytes

Like machine gun bulletsFast: Speeds up to 9953 MbpsSupports Quality of Service classesUsed primarily as a backbone

technology

ATM Cell Format

Frame segment Size

Generic Flow Control Virtual Circuit (notused)

4 bit

Virtual Path Identifier 1 byte

Virtual Channel Identifier 2 bytesPayload Type Identifier 3 bitCell Loss Priority 1 = discard eligible 1 bitHeader Error CorrectionData 48 bytes

ATM Traffic Classes (QoS)

Constant Bit Rate (CBR) Real time voice & video

Variable Bit Rate – real time (rt-VBR)

Compressed video & LAN

Variable Bit Rate – non real time (nrt-VBR)

LAN internetworking

Available Bit Rate (ABR) Non mission critical bursty Traffic

Unspecified Bit Rate (UBR)

No guarantee, e-mail, bulk file transfers

Class of Service CoS) and Quality of Service (QoS)

In an enterprise network, class of service (CoS) differentiates high-priority traffic from lower-priority traffic. Tags may be added to the packets to identify such classes, but they do not guarantee delivery as do quality of service (QoS) functions, which are implemented in the network devices.

TechEncyclopedia, 2003(class of service)

QoS

Layer 4 Responsibilities:Connection

Establish and release connectionsControl between endpoints to avoid

overflowMultiplexingCrash recovery (protection buffering)Data transferPacket splittingExpedited delivery

Transport - Layer 4

The transport layer is responsible for overall end to end validity and integrity of the transmission. The lower data link layer (layer 2) is only responsible for delivering packets from one node to another. Thus, if a packet gets lost in a router somewhere in the enterprise internet, the transport layer will detect that. It ensures that if a 12MB file is sent, the full 12MB is received.

TCP and UDP

Transmission Control Protocol

Connection oriented

Assures that packets arrive in order and that they are correct.

User Datagram Protocol

Connectionless

Sends packets out without confirming that they arrive

TCP Header (layer 4)

Source port (16 bits) Ports of communicating processes

Destination port (16 bits) “

Sequence Number (32 bits) Location of current fragment inmessage

Acknowledgement Number (32 bits) Number of frame to beacknowledged next

Offset Number of 32 bit words in header

Reserved Not used

Flags

Window Number of frames sender canaccept without buffer overflow

Checksum (16 bits)

Urgent Pointer

Ethernet/TCP/IP Header Structure

UDP Routing

Layer 5 Responsibilities

Dialog managementSynchronization of checkpoints for

error recoveryActivity management to assure

complete action messages

Session - Layer 5

Coordinates communications. Determines one-way or two-way communications and manages the dialogue between both parties; for example, making sure that the previous request has been fulfilled before the next one is sent. It also marks transmitted data with checkpoints to allow for fast recovery in the event of a connection failure.

Example: Ethernet/TCP/IP Stack

OSI Layer Internet Protocols 5-7. User Layers

File Trans-fer (FTP)

Simple Mail Transfer (SMTP)

TELNET Routing Information (RIP)

Simple Network Management (SNMP)

4.Transport Transmission Control (TCP)

User Datagram (UDP)l

3. Network Address Resolution (ARP)

Internet Protocol (IP)

Internet Control Message (ICMP)

2.Data Link Ethernet, Token Ring, etc.

1.Physical Twisted Pair, Fiber, Coax, Wireless

Backbone Protocols

Out to the WAN “cloud”

Station

Router/Gateway

Firewall

WAN

CSU/DSU

LAN Backbone

CSU/DSU:Digital Service Unit/Channel Service Unit

CSU/DSU Wide area access

The Channel Service Unit terminates the external line at the customer's premises. It also provides diagnostics and allows for remote testing.

The Digital Service Unit does the actual transmission and receiving of the signal and provides buffering and flow control. The DSU and CSU are often in the same unit.

Dual Ring Topologies(FDDI & SONET)

Dual Ring Operation

Rerouted Ring

FDDIFiber Distributed Data Interface

Common Backbone Technology Two Fiber CablesDual Ring Configuration4500 byte frame limit100 MbpsPriority AccessMultiple Frame Transmission200 km (single mode fiber)

SONETSynchronous Optical NETwork

Backbone technology used by phone company.

Layer “1” Externally synchronized

810 byte frameDual ring topologyTime division multiplexing

Multiple simultaneous data streams

SONET CIRCUITS

Service Speed (Mbps) VT-1.5 1.7OC-1 STS-1 51.84OC-3 STS-3 155.52 (3 STS-1s)OC-12 STS-12 622.08 (4 STS-3)OC-48 STS-48 2488.32 (16 STS-3)OC-192 STS-192 9953.28 (64 STS-3)OC-768 STS-768 39813.12 (256 STS-3)

OC (Optical Carrier) refers to the optical signal, and STS (Synchronous Transport Signal) refers to the electrical signal

ATMAsynchronous Transfer mode

53 byte cell 5 byte header / 48 bytes of data

Single path for all packets in a message Dedicated circuit

Quality of Service Priorities

Typical SONET and ATM use as backbone technologies

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Inter-networking