CSCE 3530: Network Edge and Core Vocabulary

Course Overview and Fundamental Internet Structure

• Architectural Components of the Internet:

  • The Internet is composed of diverse network types, including mobile networks, home networks, enterprise networks, local or regional ISPs, national or global ISPs, datacenter networks, and content provider networks.

  • From a structural standpoint, the network is divided into three primary components:

  • Network Edge: Comprises host devices, classified into clients and servers. Servers are predominantly housed within specialized data centers.

  • Access Networks: Consists of wired and wireless communication links that physically connect host devices at the edge to the network core.

  • Network Core: Consists of a mesh of interconnected routers that establish a global "network of networks."

Host Perspective and Packet Transmission Mechanics

• Application Message Chunking:

  • An application on a host generates a message that is divided into smaller discrete units called packets.

  • Each packet has a designated length measured as $L$ bits.

• Transmission Parameters:

  • Packets are injected into the access network across a physical communication link operating at a transmission rate $R$ bits per second ($\text{bits/sec}$), which is also referred to as the link bandwidth.

• Packet Transmission Delay Formula:

  • The total time required to transmit a single packet of length $L$ bits onto a link with transmission rate $R$ is defined by:   $\text{Time to transmit a packet} = \frac{L}{R}$

  • When transmitting multiple sequential packets (such as two packets of length $L$ bits each), each individual packet experiences a transmission time of $\frac{L}{R}$.

Access Network Technologies and Architecture

• Access Network Classifications:

  • Edge devices connect to the network core through various access media, including cable-based access, telephone line-based access, wireless access, cellular access, and satellite access.

  • Access networks are characterized by their bandwidth capacity and whether the physical medium provides dedicated access to a single host or shared access among multiple hosts.

• Cable-Based Access Networks:

  • Uses Frequency Division Multiplexing (FDM) to divide the shared coaxial cable spectrum into distinct frequency bands:

  • Video Channels: Allocated to specific frequency bands (e.g., Channels $1$, $2$, $3$, $4$, $5$, and $6$).

  • Data Channels: Allocated to distinct frequency bands (e.g., Channels $7$ and $8$).

  • Control Channels: Allocated to dedicated control bands (e.g., Channel $9$).

  • Network Topology: User premises contain a splitter connected to a cable modem, running over coaxial cable to an Internet Service Provider (ISP) cable headend.

  • Transmission Characteristics:

  • Asymmetric transmission speeds:

    • Downstream transmission rate: $40\text{ Mbps}$ to $1.2\text{ Gbps}$.

    • Upstream transmission rate: $30\text{ Mbps}$ to $100\text{ Mbps}$.

  • Shared physical access medium among multiple subscribers, operating with guaranteed baseline performance.

• Wireless Access Networks:

  • Wireless Local Area Networks (WiFi):

  • Governed by standards including $802.11\text{b}$, $802.11\text{g}$, and $802.11\text{n}$.

  • Operating range: Within or around a building (approximately $100\text{ ft}$).

  • Transmission rate to the Internet: $11\text{ Mbps}$ to $450\text{ Mbps}$.

  • Wide-Area Cellular Networks:

  • Provided by commercial cellular operators using $3\text{G}$, $4\text{G}$, and $5\text{G}$ technologies.

  • Operating range: Covers distances spanning tens of miles.

  • Transmission rate to the Internet: Tens of Mbps ($\text{10's Mbps}$).

  • Shared access medium operating without guaranteed baseline performance.

• Residential Access Networks:

  • Frequently combine routing, firewalling, Network Address Translation (NAT), and wireless access points into a single physical box.

  • Connects to the cable headend via a cable modem and distributes local connectivity through:

  • Wired Ethernet operating at $1\text{ Gbps}$.

  • WiFi wireless access point operating at $54\text{ Mbps}$ to $450\text{ Mbps}$.

• Enterprise Access Networks:

  • Deployed by corporate entities, universities, and government agencies.

  • Consists of a hybrid mix of wired Ethernet and wireless WiFi technologies.

  • Configured as a hierarchy of Ethernet switches connecting enterprise mail and web servers, linking to an enterprise router connected directly to an ISP.

• Datacenter Access Networks:

  • Interconnects hundreds to thousands of servers to one another and to the global Internet.

  • Employs high-bandwidth wired links ranging from $1\text{ Gbps}$ to hundreds of Gbps ($\text{100s Gbps}$).

  • Arranged in intricate topologies to maximize internal bandwidth and minimize transmission latency (e.g., Google Datacenter located in Council Bluffs, Iowa).

The Network Core, Routing, and Forwarding

• Network Core Definition:

  • The network core is a mesh of interconnected routers responsible for moving data packets end-to-end through the network.

• Core Functions:

  • Moving packets from source to destination relies on two fundamental network-core functions: routing and forwarding.

• Forwarding vs. Routing Distinction:

  • Forwarding (Switching): A local router action that moves an arriving packet from the router's incoming link interface to the appropriate outgoing link interface.

  • Analogy: Making a specific local maneuver or turn at an individual intersection (e.g., navigating local roads in Sacramento such as North Natomas, Arden-Arcade, or Rosemont).

  • Routing: A global network action that determines the complete end-to-end path taken by packets from a source to a destination using routing algorithms.

  • Analogy: Planning an entire long-distance highway travel route across regions (e.g., driving $31\text{ hr}$ over $2039\text{ miles}$, $25\text{ hr}$ over $1664\text{ miles}$, or $27\text{ hr}$ over $1790\text{ miles}$).

• Mechanism of Forwarding Tables:

  • Every arriving packet contains a header specifying a destination address (e.g., 0111).

  • The router reads the destination address in the packet header and indexes its local forwarding table to select the target output link interface.

  • Routing algorithms dynamically compute and write the mapping values contained within local forwarding tables.

  • Example Local Forwarding Table Mapping:

  • Packet Header 0100 $\rightarrow$ Output Link $3$

  • Packet Header 0101 $\rightarrow$ Output Link $2$

  • Packet Header 0111 $\rightarrow$ Output Link $2$

  • Packet Header 1001 $\rightarrow$ Output Link $1$

  • Under this mapping, an arriving packet with header 0111 is forwarded directly to output link $2$.