Introduction to DOCSIS, Network Protocols, OSI Model

Transmission Control Protocol (TCP)

A connection oriented transport protocol that checks if data has been received.

User Datagram Protocol (UDP)

A connectionless oriented transport protocol that does not check if data was received.

Protocol Suite

A group of protocols that are used together.

Transport Layer Security (TLS)

A more advanced version of SSL.

Dynamic Host Configuration Protocol (DHCP)

A protocol that allows a server to assign internet configuration to a client.

File Transfer Protocol (FTP)

A protocol that uses TCP to transfer files from one computer to another.

Hyper Text Transfer Protocol (HTTP)

A protocol used by Internet browsers to send and receive webpage data.

Internet Message Access Protocol (IMAP)

A protocol used to access email on a server while the email remains on the server.

Post Office Protocol ver 3 (POP3)

A protocol used to download email from an email server to be saved on the client.

Simple Mail Transfer Protocol (SMTP)

A protocol used to send mail between email servers.

Secure Shell (SSH)

A secure way of accessing and controlling hosts remotely.

Secure Socket Layer (SSL)

A security protocol that encrypts data before transmission using an algorithm.

Network Protocols

A set of rules that govern the way computers communicate across a network.

Internet Control Message Protocol (ICMP)

A way to detect what other devices are connected to the network.

Internet Group Management Protocol (IGMP)

A way to establish mulitcast groups so that messages can be sent to multiple hosts at the same time.

Network Layer

Adds logical addressing (network addresses) and chooses the best route. IP, ICMP, and IGMP exist at this layer. Routers, multilayer, switches, and firewalls work at this layer.

Network Time Protocol (NTP)

Allows hosts on a network to synchronize their clocks.

Telnet

An unsecured way of accessing and controlling hosts remotely.

Layer 7

Application

Layer 7 & Layer 6 Network Devices

Application proxy

TCP/IP Model

Application, Transport, Internet, Network Access

Why are the data throughput rates for both downstream and upstream in DOCSIS networks asymmetrical?

Because the narrower bandwidths and lower orders of modulation for the return path carriers cause the DOCSIS downstream and upstream data raters to be unequal or asymmetrical

Physical PDU (Protocol Data Unit) Type

Bits

What Criteria does the DOCSIS certification process ensure

Compliance with the DOCSIS standard and interoperability between suppliers.

Which DOCSIS version was the first to provide an option for raising the top frequency of the upstream spectrum to 85 megahertz (MHz) in order to create enough bandwidth for upstream carriers from modems running on previous DOCSIS modems?

DOCSIS 3.0

Layer 2

Data Link

Application Layer

Enables applications on a network node (device) to request network services such as file transfers, email, and database access.

Layer 6 Protocols/Key Characteristics

Encryption, compression, character sets, multimedia formats, MIME types, codecs, etc

Session Layer

Establishes and controls data communication between applications operating on two different devices.

Secure FTP (SFTP)

FTP that uses SSL for security.

Trivial FTP (TFTP)

FTP that uses UDP so it is faster but less reliable.

Layer 5 & Layer 4 Network Devices

Firewalls

Data Link PDU Type

Frame

Where do DOCSIS modems receive their configuration files, billing system messages and access control messages from?

From the CMTS (headend) which interfaces with the operations support system (OSS) and acts as a proxy or messenger that transfers messages and files between the modems and the respective servers.

HTTP Secure (HTTPS)

HTTP using SSL to secure the transmission of data.

Layer 7 Protocols/Key Characteristics

HTTP, FTP, SMTP, IMAP, etc

Which Layers of the Open Systems Interconnection (OSI) reference model are specific to cable networks and are present only between DOCSIS modems and the CMTS?

Layers 1-4 (Physical Layer, Data Link layer, Network layer, and transport layer) are applied between the DOCSIS Modem and CMTS.

Simple Network Management Protocol (SNMP)

Lets network administrators set up alerts to monitor and manage the state of a network.

Session, Presentation, and Application PDU Type

Message

Layer 3

Network

What features were introduced with the 3.1 Version of (DOCSIS 3.1) to increase the downstream and upstream data throughput?

Orthogonal frequency division multiplexing (OFDM) and low-density parity-check (LDPC).

Network PDU Type

Packet

Transport Layer

Performs the actual establishment, maintenance, and tear down of the connection. Optionally divides long communications into smaller segments, including error recognition and correction, and data receipt acknowledgment. TCP

Layer 1

Physical

Layer 6

Presentation

What requirements were needed for PacketCable to deliver a quality and reliable telephone service over a DOCSIS access network?

Quality of Service (QOS) controls, enhanced security and adaptive equalization in the upstream path.

Transport PDU Type

Segment

Layer 5

Session

Data Link Layer

Structures the data into a format appropriate for the transmission medium. Adds physical addresses such as MAC addresses or frame relay data link connection identifier (DLCI) numbers.

Layer 5 Protocols/Key Characteristics

TCP and UDP port numbers

Layer 4 Protocols/Key Characteristics

TCP and UDP protocols

The First version of DOCSIS was approved as an international standard by what organization?

The International Telecommunication Union (ITU)

Which Open Systems Interconnection (OSI) reference model layers does the Media Access Control (MAC) Layer in the Data Over Cable Service Interface Specification (DOCSIS) overlap so that the media access control (MAC) can be used by the cable modem termination system (CMTS) to differentiate between cable modems?

The physical and data link layers

What communications access technology does the first version of DOCSIS (DOCSIS 1.0) use to send data upstream over the networks radio frequency (RF) return path?

Time Division Multiple Access (TDMA)

Presentation Layer

Translate application layer data into an intermediate form that both client and server can process. (Proxies and Firewalls work at this layer)

Domain Name System (DNS)

Translates a URL (www.xyz.com) into an IP address (105.56.48.254)

Physical Layer

Transmits bits (binary digits) from one device to another and regulates the transmission stream over a medium (wire, fiber optics, or radio waves) All electrical and mechanical aspects of data transmission exist at this layer, including cabling, connectors, antennas, transceivers, baseband, broadband, signaling types, voltages, waveforms, modulation, frquencies, and clock rates. NIC, hubs and repeaters work at this layer.

Layer 4

Transport